Bimetal alloy snap disc-type thermostats, such as those manufactured by Therm-O-Disc, Incorporated, provide a reliable and inexpensive method of opening and closing an electrical circuit in response to changes in surface or ambient temperatures. Changes in the thickness and composition of the bimetal alloy disc allow the thermostats to be adjusted to open and close at specified temperatures. Bimetal disc thermostats are widely used in home appliances and HVAC applications to control the flow of electrical current to fans, heating elements and a variety of other devices.
A limitation of a bimetal disc thermostat is that the bimetal disc is stressed and the thermostat eventually fails when subjected to temperatures above approximately 650° F. (343° C.). As a result, prior to the subject invention, more expensive sensors and switches have been required for higher temperature applications. An example is sensing the temperature of a flue conveying hot exhaust gas flow from a fireplace in a ventilation system such as is disclosed in McCarren Patent Application Publication No. US 2002/0014234 titled “Ventilation System and Method.”
In addition, there are a number of environments that may be within the temperature limitations of bimetal disc thermostats, but which for other reasons are unsuitable for the direct exposure of the thermostat, such as a corrosive environment, moisture or other adverse conditions.